In multicast and broadcast applications, data are transmitted from a server to multiple receivers over wired and/or wireless networks. A multicast system as used herein is a system in which a server transmits the same data to multiple receivers simultaneously, where the receivers form a subset of all the receivers up to and including all of the receivers. A broadcast system is a system in which a server transmits the same data to all of the receivers simultaneously. That is, a multicast system by definition can include a broadcast system.
Consider multicast (downlink) and multi-access (uplink) channels with one access point (AP) and several nodes. In the IEEE 802.11n draft standard, a reverse direction (RD) protocol is introduced for fast scheduling of bidirectional traffic flows within a transmission opportunity (TXOP). The reverse direction protocol permits (allows) the node, which has obtained the TXOP to grant reverse directional transmissions to another node while it is still in control of the TXOP. If the channel conditions between the nodes are inadequate (poor) then transmissions between the two nodes suffer. That suffering may be reduced data rate and/or throughput.
In the IEEE 802.11n draft standard, a reverse direction (RD) protocol has been proposed as in FIG. 1. The reverse direction protocol of the IEEE 802.11n draft standard only schedules bidirectional transmission between two nodes. Each node is both a source node and a destination node. There is no existing scheduling protocol for three-node bidirectional transmissions in IEEE 802.11 WLAN standards. FIG. 1 illustrates the conventional unidirectional cooperation using a half-duplex relay node (RN). FIG. 1a shows the first stage of communication, in which Node1 transmits (sends, communicate) data S1 to both Node2 and the RN. FIG. 1b shows stage 2 of communication, in which the RN transmits (communicates, sends) data Ŝ1 to Node2. That is, the RN transmits (communicates, forwards, sends) data S1 as Ŝ1 to Node2. Correspondingly (and not shown), in the third stage of communication, Node2 transmits (sends, communicate) data S2 to both Node1 and the RN. In the fourth stage of communication, the RN transmits (communicates, forwards, sends) data Ŝ2 to Node1. That is, the RN transmits (communicates, forwards, sends) data S2 as Ŝ2 to Node1. Thus, in the conventional approach, there are four stages (phases) to complete communications using the half-duplex RN to assist Node1 and Node2.
Network-coded three-node bidirectional cooperation with three stages (i.e., the reception of signals from nodes (source and destination) at the RN are orthogonal (separate)) has been studied, using Decode-and-Forward, Soft Decode-and-Forward, and Amplify-and-Forward in a single-antenna system, and a case when L1=L2=1 and LR=2 etc, respectively. Note that Li, i=1, 2,R represents the number of antennas at Node1, Node2 and RN respectively. The present invention uses Amplify-and-Forward for the general MIMO case with an arbitrary number of antennas at the nodes. This has not been addressed in any publications known to the Applicants.